The general principle of selecting ion exchange resin is to select the resin with large exchange capacity, easy regeneration and durability. Specifically:

(1) Exchange capacity is an important indicator of the performance of ion exchange resin. The greater the exchange is, the more ions can be adsorbed by the same volume of resin, and the greater the water production in an exchange cycle. Generally speaking, the exchange capacity of weak acid or weak base resin is larger than that of strong acid or strong base resin. In addition, in the same kind of resin, the exchange capacity is also different due to the different crosslinking degree of the resin. Generally, the resin with small cross-linking degree has large exchange capacity; The resin with high crosslinking degree has small exchange capacity. Therefore, attention should be paid to the selection of resin.

(2) The resin shall be selected according to the nature of the ions to be removed from the raw water. If only ions with weak exchange adsorption in water need to be removed, strong acid or strong alkaline resin must be selected.

(3) The resin shall be selected according to the effluent quality requirements. If only partial desalting system is required, strong acid cation resin and weak alkali anion resin can be used together. For pure water or high-purity water system that must be completely desalted, strong acid cation exchange resin with strong adsorption and basic anion exchange resin shall be used together to remove ions that are difficult to be adsorbed.

(4) The resin shall be selected according to the composition of impurities in raw water. If there is much organic matter in the raw water or the radius of ion removal is large, the resin with large cross-linking pore diameter shall be selected. Try to choose high-strength porous resin.

(5) Most of the resins used in the mixed bed are the combination of strong acid and strong alkali resins. However, it should be considered that the resin in the mixed bed is easy to be layered during regeneration. Therefore, it is required that the difference between the wet true densities of the two resins should be larger, generally not less than 15% ~ 20%. In addition, considering that the exchange flow rate is relatively large and the resin is seriously worn during the operation of the mixed bed, the wear-resistant resin should be selected.

(6) The resin shall be selected according to the process requirements of demineralized water. For example, for the double chamber bed, the strong and weak resins are used together, because the weak resin is easy to regenerate, and the quality requirements for the regenerant are relatively low. The regenerant liquid after the strong resin regeneration can be used to regenerate the weak resin, so the regenerant consumption is low and the water production cost is low.